Using percentage of cost as expense?

[W Pawlowski]

I am one man show so I am using my personal car for business.
Lets say that 90% of use is for business and 10% is for personal use.
Is there a way in GnuCash to have the automotive expense account calculate
the percentage automatically and assign 90% of what ever is entered into
this account as expense or would I have to do it manually every time I
enter my expenses?
Thank you.